The detection and evaluation of structural flaws by non-destructive use of radiation is generally known in the art, including use of microwave radiation exhibiting certain advantages over other forms of radiation such as x-ray, ultrasound and thermography radiation. Such uses of microwave radiation include emission and reflection of the radiation after interaction with the targeted material for detecting the presence or absence of a defect therein. Microwave radiation types of defect detection systems heretofore involved one or more antennas for emission of the radiation and reception of reflective radiation. Some of the advantages over the use of other forms of radiation include, avoiding use of a couplant and heat diffusion means, increasing depth of detection and avoiding the provision of radiation hazard prevention. It is therefore an important object of the present invention to enlarge evaluation of structural flaws by the advantageous use of microwave radiation as disclosed in connection with the embodiment covered in the aforementioned prior copending parent application, Ser. No. 08/798,683 now U.S. Pat. No. 5,859,535. According to the disclosure in such prior copending parent application, detection location and sizing of an internal defect in a thick non-metallic material or composite is achieved by isolating in time reflections of microwave radiation from external surfaces using Fourier transformation of frequency domain data applied in a straight forward manner.